The long-term goal of our research is to unravel the mechanism regulating the clustering and postsynaptic targeting of g-aminobutyric acid type A (GABAA) receptors. These receptors are hetero-pentameric chloride channels and they mediate most inhibitory neurotransmission in the brain. GABAA receptor subtypes distinguished by their subunit composition are differentially expressed at the regional and cellular level. Differential localization of GABAA receptors is implicated in regulation of synaptic efficacy of GABAergic transmission and pathological changes in receptor localization are implicated in debilitating disorders such as epilepsy and anxiety. The factors and signaling pathways that determine receptor clustering and localization are largely unknown and shall be identified as part of this proposal. Most GABAA receptor subtypes are clustered at postsynaptic sites by a mechanism that requires the g2 subunit and the clustering protein gephyrin. Different a subunits might target receptors to different types of synapses. However, it is not known how GABAA receptors are linked to gephyrin and to the subsynaptic cytoskeleton. We hypothesize that synaptic localization is mediated at least in part by postsynaptic proteins that interact with cytoplasmic protein domains of the g2 subunit. To test this hypothesis we will map g2 subunit domains that mediate postsynaptic localization in neurons. Loss of the g2 subunit in vivo is associated with a reduced GABAA receptor channel conductance. It has been postulated that this reduced channel function during neural development might contribute to loss of GABAA receptor clusters in g2 subunit deficient neurons. Genetic approaches will be used to determine whether receptor activation is required for clustering of GABAA receptors. Finally, novel GABAA receptor binding proteins that interact with the g2 or a2 subunits will be analyzed with respect to their role in receptor clustering and localization. These studies will significantly advance our understanding of the regulation of GABAergic neurotransmission and identify new potential drug targets for the treatment of mental and neurological disorders such as anxiety and epilepsy.